.arcconfig

discovery: stop direct use of attribute of partialdiscovery

Instead of accessing `undecided` directly for ui display purposes,
we introduce a `stats()` method that could be extended in the future with
more interesting information.

This is in preparation for a forthcoming Rust version of this object.
Indeed, attributes and furthermore properties are a bit complicated for
classes in native code.

We could go further and rename `undecided` to mark it private, but `_undecided`
is already taken as support for `_undecided` lazyness.

{
    "conduit_uri": "https://phab.mercurial-scm.org/api",
    "repository.callsign": "HG",
    "arc.land.onto.default": "@",
    "base": "hg:.^"
}